Food Proportions and calculating fat calculations?

I have a question of how to properly account for fats in a meat. Lets say a 4 oz piece of chicken is 120 cal of protein and 20 fat cal. Now when i grill it, will that fat content be reduced dramatically? i know it helps but is it like half the cal or how can i make a ballpark figure for fat content in meat after preperation. any websites to figure this stuff out?